U.S. patent number 5,909,072 [Application Number 08/445,023] was granted by the patent office on 1999-06-01 for brushless three-phase dc motor.
This patent grant is currently assigned to Papst Licensing GmbH. Invention is credited to Rolf Muller.
United States Patent |
5,909,072 |
Muller |
June 1, 1999 |
Brushless three-phase dc motor
Abstract
A three-phase brushless dc motor includes a permanent-magnet
rotor magnet arrangement having at least four poles and a
Y-connected, or star-connected, three-phase stator winding. The
winding's phases are arranged non-overlapping in slots of a slotted
stator, the currents flowing in the three phases being controlled
via at least three semiconductor elements by at least three
magnetic-field-sensitive rotor position sensors. Each sensor is
associated with a respective two of the winding's three phases and
triggers a commutation which switches off the current in one of the
associated two phases and switches on the current in the other of
the associated two phases. The sensors are located to sense the
permanent-magnet flux emanating from the rotor poles themselves.
The rotor position sensors are provided at special angular
locations on the stator. Each sensor is provided at an angular
location at which there is not to be found, neither prior to nor
subsequent to the commutation associated with that sensor, any
energized stator pole; this may mean that the sensor location is
(i) an angular location at which no energizable stator pole
whatever is present, and it may mean that the sensor location is
(ii) an angular location at which an energizable stator pole is in
fact present, but during motor operation this energizable stator
pole is in an unenergized state prior to a commutation associated
with the particular sensor in question and likewise is in
unenergized state subsequent to that commutation.
Inventors: |
Muller; Rolf (Munich,
DE) |
Assignee: |
Papst Licensing GmbH
(DE)
|
Family
ID: |
27544350 |
Appl.
No.: |
08/445,023 |
Filed: |
May 19, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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154383 |
Nov 18, 1993 |
5418416 |
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902474 |
Jun 19, 1992 |
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620645 |
Nov 30, 1990 |
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066471 |
Jun 26, 1987 |
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607688 |
May 7, 1984 |
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Foreign Application Priority Data
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Sep 5, 1983 [DE] |
|
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P 33 31 940 |
Sep 5, 1983 [DE] |
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G 83 25 441 |
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Current U.S.
Class: |
310/68B; 310/186;
310/173; 318/400.28; 310/216.067; 318/400.29 |
Current CPC
Class: |
H02K
29/08 (20130101); H02K 1/146 (20130101); H02K
1/148 (20130101); H02K 29/03 (20130101); H02K
21/14 (20130101); H02K 1/02 (20130101) |
Current International
Class: |
H02K
29/08 (20060101); H02K 1/14 (20060101); H02K
21/14 (20060101); H02K 29/06 (20060101); H02K
1/00 (20060101); H02K 1/02 (20060101); H02K
29/03 (20060101); H02K 029/06 (); H02K
029/00 () |
Field of
Search: |
;318/254,138
;310/68B,186,259,173,135,159,156 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: LaBalle; Clayton
Assistant Examiner: Mullins; Burton S.
Attorney, Agent or Firm: Fitch, Even, Tabin &
Flannery
Parent Case Text
This application is a Continuation of application Ser. No.
08/154,383, filed Nov. 18, 1993, now U.S. Pat. No. 5,418,416, which
is a Continuation of application Ser. No. 07/902,474, filed Jun.
19, 1992, now abandoned, which is a Continuation of application
Ser. No. 07/620,645, filed Nov. 30, 1990, now abandoned, which is a
Continuation of application Ser. No. 07/066,471, filed Jun. 26,
1987, now abandoned, which is a Continuation of Ser. No.
06/607,688, filed May 7, 1984, now abandoned.
Claims
What is claimed is:
1. A three-phase collectorless dc motor comprising:
a permanent-magnet rotor magnet arrangement having at least two
pole pairs; and
a star-connected three-conductor stator winding, the winding's
conductors being arranged non-overlapping in slots of a slotted
stator,
wherein currents in the stator windings are controlled via at least
three semiconductor elements in response to at least three output
signals from a rotor position detecting circuit, said circuit
including a plurality of magnetic-field-sensitive position sensors
which are controlled by the rotor magnet arrangement,
wherein the position sensors are distributed along the stator's
circumferential direction in such a manner relative to the stator
winding's conductors that, at each commutation operation, each
position sensor which effects the commutation of the winding's
current from one to another of the winding's conductors is provided
in a region of the stator in which a current-carrying coil is
present neither immediately before nor immediately after the
commutation operation;
wherein each of the position sensors is located substantially on a
radial-symmetry axis of a stator pole carrying a coil of the one
phase that is not involved in the commutation operation triggered
by that particular position sensor.
2. A three-phase collectorless dc motor according to claim 1,
wherein the number of stator poles stands in the ratio 3:4 to the
number of rotor poles and each of the stator poles has a breadth of
substantially 180 degrees-el.
3. A three-phase collectorless dc motor according to claim 1,
wherein, considered in the circumferential direction, each position
sensor is located substantially midway between neighboring coils
between which the commutation of the winding's current occurs under
the influence of the position sensor in question.
4. A three-phase collectorless dc motor according to claim 1,
wherein the motor produces at least three pulses per 360 degrees
electric.
5. A three-phase collectorless dc motor according to claim 4,
wherein the motor is a six-pole motor with at least four magnetic
rotor pole pairs.
6. A three-phase collectorless dc motor according to claim 1,
wherein at the air gap the space remaining in the circumferential
direction between each two neighboring stator poles is
substantially filled up by an unwound auxiliary stator pole.
7. A three-phase collectorless dc motor comprising:
a permanent-magnet rotor magnet arrangement having at least two
pole pairs; and
a star-connected three-conductor stator winding, the winding's
conductors being arranged non-overlapping in slots of a slotted
stator,
wherein currents in the stator windings are controlled via at least
three semiconductor elements in response to at least three output
signals from a rotor position detecting circuit, said circuit
including a plurality of magnetic-field-sensitive position sensors
which are controlled by the rotor magnet arrangement,
wherein the position sensors are distributed along the stator's
circumferential direction in such a manner relative to the stator
winding's conductors that, at each commutation operation, each
position sensor which effects the commutation of the winding's
current from one to another of the winding's conductors is provided
in a region of the stator in which a current-carrying coil is
present neither immediately before nor immediately after the
commutation operation;
wherein the stator has a succession of poles which are integrally
connected to one another, wherein intermediate each pole and the
next there is an auxiliary pole;
wherein the auxiliary poles are provided with recesses for
accommodating the position sensors.
8. A three-phase collectorless dc motor according to claim 7,
wherein the auxiliary poles are unwound poles.
9. A three-phase collectorless dc motor according to claim 7,
wherein the auxiliary poles are inserted into recesses of the
stator.
10. A three-phase collectorless dc motor according to claim 7,
wherein each auxiliary pole is in the form of a one-piece pole
body.
11. A three-phase collectorless dc motor according to claim 10,
wherein the auxiliary poles are fabricated from solid material.
12. A three-phase collectorless dc motor according to claim 11,
wherein the auxiliary poles are sintered bodies.
Description
BACKGROUND OF THE INVENTION
The invention concerns a three-phase brushless dc motor with a
permanent-magnet rotor magnet arrangement having at least two pole
pairs and a star-connected, three-phase stator winding, the
winding's phases being arranged non-overlapping in slots of a
slotted stator, with their currents being controlled via at least
three semiconductor elements by at least three
magnetic-field-sensitive position sensors, the latter in turn being
controlled by the rotor magnet arrangement.
With motors controlled in this manner, especially in the case of
motors operating at high power, there arises the problem of the
field from the stator winding influencing the
magnetic-field-sensitive position sensors although in theory, of
course, these sensors should be responsive only to the rotor magnet
poles. As a result of such influence, the commutation time points
are in undesirable fashion shifted from their predetermined optimal
times of occurrence. This is because any part of the stator-winding
field that happens to be incident upon one of the rotor-position
sensors is wrongly interpreted by the latter as part of the flux
coming from a rotor-magnet pole. Accordingly, this problem becomes
more severe, the higher the winding's current.
SUMMARY OF THE INVENTION
Therefore an object of the invention is to so design a dc motor of
the stated type as to substantially prevent a shifting of the
commutation time points under the influence of the currents flowing
in the stator winding.
According to the invention this object is achieved in a
surprisingly simple manner by choosing the respective angular
locations for the position sensors in a special manner relative to
the coils of the three phases. Usually, each position sensor
triggers or in another manner commands commutation or switchover of
the winding's current from a first to a second one of two phases
associated with that particular position sensor. In accordance with
the present invention, in such event, each sensor element is placed
at an angular location on the stator at which there is not to be
found, neither prior to nor subsequent to the commutation
associated with that sensor, any energized stator pole. This may
mean that such sensor's location is (i) an angular location that is
circumferentially intermediate two circumferentially spaced,
neighboring energizable stator poles, to thereby be an angular
location at which an energizable stator pole is not present; and
the foregoing may mean that the sensor's location is (ii) an
angular location at which an energizable stator pole is indeed
present, but during motor operation this stator pole is in an
unenergized state prior to a commutation associated with the sensor
in question and likewise is in unenergized state subsequent to that
commutation.
With the motor according to the invention the
magnetic-field-sensitive position sensors remain uninfluenced by
the stator winding's field during the commutation. Even in the case
of higher winding currents there does not occur an undesired
displacement of the commutation time points.
In accordance with a further feature of the invention the number of
stator poles stands in the ratio 3:4 to the number of rotor poles,
each of the stator poles having a breadth of substantially
180.degree.-el. As a result a chording is avoided. A particularly
high efficiency is achieved. The torque developed by the motor is
substantially uniform.
It has proved especially advantageous to locate each position
sensor substantially midway, considered in the circumferential
direction, between those neighboring coils as between which the
commutation of the winding's current occurs under the influence of
that particular position sensor.
According to a further embodiment each position sensor can also be
located substantially on the radial symmetry axis of a stator pole
carrying a coil of the one phase that is not involved in the
commutation operation triggered by that particular position
sensor.
The motor can be designed as a three-pulse motor or else as a
six-pulse motor, in the latter case it having preferably at least
four magnetic pole pairs.
Preferably, at the air gap, the space remaining in the
circumferential direction between each two neighboring, preferably
180.degree.-el.-wide stator poles is substantially filled up by an
unwound auxiliary stator pole. The auxiliary stator poles very
effectively avoid a magnetic jolt, because an approximately uniform
induced voltage is obtained over a relatively large angle, which
means a uniform torque at constant current. Without such auxiliary
poles between 180.degree.-el.-wide stator poles, in the case of a
ratio of stator poles to rotor poles of 3:4 the stator poles would
be, functionally, wider than 180.degree.-el. because a great part
of the rotor's magnetic field appearing in the pole gaps, would be
attracted to the stator poles. There would set in an undesired
manner a chording action.
In the case of the motors set forth above--but also in general in
the case of brushless dc motors with a permanent-magnet rotor
magnet arrangement and a slotted stator carrying a stator winding
wound without overlap, the stator having a succession of poles that
are of one piece with one another, e.g. stamped out in conventional
manner from Dynamo sheet metal--it is desirable that, on the one
hand, the slot openings be kept small but, on the other hand, that
the slot openings be large enough to facilitate insertion of the
winding's constituent coils during the fabrication. In accordance
with the invention this problem is solved in that the auxiliary
poles are provided as separate parts which can be inserted between
main poles and be connected to the stator afterwards. During the
winding procedure the auxiliary poles are left off. As a result the
winding can be installed in the stator slots unproblematically. The
auxiliary poles are installed only when the stator windings have
been formed. These later installable auxiliary poles can
advantageously form the aforesaid unwound auxiliary poles.
In accordance with a further feature of the invention the auxiliary
poles are insertable into recesses of the stator winding's core.
Whereas the latter advantageously involves, in conventional manner,
a stack of sheet metal, each auxiliary pole is preferably formed as
a one-piece pole body. In particular the auxiliary poles can be
formed from solid material or as sintered bodies. Because the
auxiliary poles, in correspondence to their relatively short
circumferential extent, accept only a relatively small magnetic
flux, eddy-current losses, in particular, remain low even in the
case of solid auxiliary poles. Manufacture from sintered iron has
the advantage that by means of powder-metallurgy techniques very
exact shapes can be manufactured without there being a need to
thereafter do further material-removing machining work.
Furthermore, for electro-technical applications there are
commercially available also suitable siliconized iron types, such
as e.g. from the Vakuumschmelze Company under the trade name
"Trafoperm".
The auxiliary poles can advantageously be provided with recesses
suited for accommodating the position sensor; the latter can
involve, in particular, Hall generators, Hall-IC's or similar
magnetic sensors. In the case that sintering techniques are used
such recesses can be formed in particularly simple manner.
The invention is explained in greater detail below with respect to
preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts, schematically, a sectional view of a dc motor
according to the invention,
FIG. 2 is a view similar to FIG. 1 for a modified embodiment of the
invention,
FIG. 3 is a sectional view through an auxiliary pole corresponding
to the line III--III of FIG. 2, and
FIG. 4 depicts a set of waveforms referred to in describing the
preferred mode of operation of the motor.
DESCRIPTION
The three-phase brushless dc motor of FIG. 1 has a rotor 10,
rotatably mounted in a manner not illustrated in detail, with a
permanent-magnet rotor magnet arrangement 11. The rotor magnet
arrangement 11 is preferably formed from a rubber-magnet strip,
i.e. a one-piece strip made of a mixture of hard ferrite, e.g.,
barium ferrite, and elastic material. The magnet strip is radially
magnetized; its magnetization pattern has the shape of a trapezoid,
or approximately a trapezoid, extending over the pole pitch, with
relatively small pole gaps. It forms in the illustrated embodiment
four pole pairs which at their outer peripheral surfaces
constitute, alternately, magnetic north poles 12 and magnetic south
poles 13. It is to be understood that other magnetic materials can
be used too, and that the rotor magnet arrangement can also be
assembled from individual magnetic plates.
The rotor 10 is encircled by a stator 15, preferably in the form of
a laminated stack of sheet metal, forming a cylindrical air gap 16.
Only one-half of the stator 15 is depicted; the other half is
configured symmetrically in correspondence thereto. The stator 15
has six T-shaped main poles 17. The pole faces 18 of the main poles
17 face the air gap 16 and each extends for an angle of
180.degree.-el., i.e., the width of each of the six main poles is,
at the air gap 16, equal to the width of each of the eight rotor
poles 12, 13. In this way, at the air gap 16, there result between
the main poles 17 gaps which are each 60.degree.-el. wide. These
gaps are substantially filled up by auxiliary poles 19, i.e., the
pole faces 20 of the auxiliary poles 19 extend from a breadth of
almost 60.degree.-el.; they end at a small distance, in the
circumferential direction, from the respective neighboring
main-pole face 18. Each of the main poles 17 carries a stator coil,
of which in FIG. 1 the three stator coils 22, 23, 24 are depicted.
Corresponding stator coils--which can be connected in series with
their respective diametrically opposite stator coils 22 or 23 or
24--are provided on the three non-illustrated main poles. The
stator coils altogether form a star-connected, three-phase stator
winding whose constituent coils do not overlap one another. As a
result the axial ends of the coils are specially short in the axial
direction, which is advantageous not only for spatial reasons but
also leads to low winding resistance. In the arrangement of FIG. 1
the common or star junction of the stator winding is connected via
a line 25 to the positive side +U.sub.B of a voltage source; the
star junction is connected to a respective first end of each of
coils 22, 23, 24. The other end of each of these coils is
connected, via its associated series-connected, diametrically
opposite coil (not shown) to a respective semiconductor switch 26,
27 or 28, and then via a respective one of these switches to the
negative side -U.sub.B of the voltage source. For the commutation
operations the semiconductor switches 26, 27, 28 are controlled by
the magnetic-field-sensitive position sensors 30, 31, 32. The
position sensors can in particular be Hall generators or Hall IC's
which are, in turn, controlled by the rotor magnet arrangement
11.
As a result of the given geometry, the position sensor 30 can be
arranged on the stator at eight different angular locations along
the air gap 16, of which four locations are denoted by 30a, 30b,
30c and 30d in FIG. 1. The other four possible angular locations
are located diametrically opposite to respective ones of the
locations just stated. It has been found that one can in a simple
way avoid the position sensors being exposed to the field from the
stator coils, and avoid the resulting undesired shifting of the
commutation time points, by locating the position sensors 30, 31,
32 at the air gap 16 at specially determined angular locations. As
defined earlier in the general discussion of the invention further
above, each sensor is placed at an angular location at which there
is not to be found, neither prior to nor subsequent to the
commutation commanded by that sensor, any energized stator pole; as
stated earlier and as will become clearer below, this may mean that
such sensor's location is (i) an angular location at which no
energizable stator pole whatever is present; likewise, this may
mean that the sensor's location is (ii) an angular location at
which an energizable stator pole is in fact present, but during
motor operation this stator pole is in unenergized state prior to a
commutation associated with the sensor in question and likewise is
in unenergized state subsequent to that commutation. The position
sensor 30 triggers or commands the commutation from the stator coil
22 to the stator coil 23, rendering the semiconductor switch 26
non-conductive and rendering the semiconductor switch 27
conductive. The criterion stated just above is fulfilled for
position sensor 30 if the latter is arranged at the angular
positions 30a or 30c; in contrast, it is not fulfilled at the
positions 30b and 30d. The position 30a is located on the radial
symmetry axis of the main pole 17 carrying the coil 24, i.e., a
coil of the one phase that is not involved in the commutation
operation triggered by position sensor 30. The second advantageous
position 30c for the position sensor 30 is at the auxiliary pole 19
located angularly intermediate the two stator coils 22 and 23;
these are coils of the two phases that are involved in the
commutation or switchover commanded by position sensor 30. In
contrast, the two further positions 30b and 30d for the position
sensor 30 do not satisfy the aforesaid criterion. At position 30b
the position sensor 30 would be exposed to the magnetic field from
coil 23 after the commutation operation, whereas at position 30d
the position sensor 30 would be exposed to the field from coil 22
prior to the commutation in question.
Corresponding remarks apply to the other two position sensors 31,
32; the positions in principle possible for these within the
illustrated region of 180.degree.-mech. are denoted by 31a, 31b,
31c, 31d and 32a, 32b, 32c, 32d, respectively. Here again, of these
positions only the positions 31a and 31c for sensor 31 and 32a, 25
and 32c for sensor 32, fulfill the criterion in question.
The foregoing discussion of FIG. 1 presupposes a certain known type
of three-pulse operation, i.e. the rendering conductive at any
given time of only one of the winding's three phases, the flow of
current through each of the winding's phases always being in the
same direction, as depicted graphically in FIG. 4 and reviewed
further below. The stator coils 22, 23, 24, and their
non-illustrated diametrically opposite partners, and the
semiconductor switches 26, 27, 28 accordingly form a circuit
configuration which can be designated as half of a bridge circuit.
However, the invention is not limited thereto. The described motor
can instead operate with a full bridge circuit permitting a
reversal of the direction of the current in each phase (such a full
bridge circuit is for example known from FIG. GB of DE-OS 30 44
027), and the motor can thusly be operated in six-pulse fashion, in
which case at any given time two of the winding's phases carry
current simultaneously. Referring to FIG. 1 it may be noted that,
in the case of six-pulse operation, only the positions 30c, 31c,
32c fulfill the inventive criterion.
The use of at least eight permanent-magnet poles has furthermore
the advantage that the forces exerted on the rotor shaft are
symmetrical with respect to the motor axis.
The Hall element positions as discussed above have particular
significance when the motor of FIG. 1 is operated in the particular
type of three-pulse fashion shown in FIG. 4, although persons
skilled in the art will understand that other and equivalent
contacts may also be employed. FIG. 4A shows the output voltage of
one of the motor's three Hall elements. This voltage is cyclical
and has a period equal to 360.degree.-electrical. The FIG. 4A
voltage is applied to a comparator, or other conventional pulse
shaper, to yield the better defined voltage waveform of FIG. 4B,
each pulse of which lasts for 180.degree.-electrical. The same
applies for the other two Hall elements, but preferably their
respective pulse trains are phase-shifted one from the other by
120.degree.-electrical, as shown for the three Hall elements in
FIG. 4C, i.e., due to the locations of these three elements. The
set of three pulse trains of FIG. 4C is applied to a logic circuit
to generate three different pulse trains shown in FIG. 4D. The
pulses in each of these trains have a duration of 120.degree.-el.,
a period of 360.degree.-el., and the three pulse trains are
phase-shifted one from the next by 120.degree.-el. Each of the
three pulse trains is used to render conductive a respective one of
the three transistors 26, 27, 28, so that FIG.4D also represents
the respective conduction times of these transistors. FIGS. 4E1,
4E2, 4E3 depict the theoretically possible and (in the shaded
areas) the actual torque contributions of respective ones of the
three coil systems, the type of three-pulse operation shown in FIG.
4 being the type that utilizes less than the full torque
theoretically possible. Namely, if the respective transistor of one
of these phases were always conductive, the associated torque
contribution would be sometimes in the correct rotation direction
(shown as positive) and sometimes in the non-desired rotation
direction (shown as negative); therefore, in this example, the
transistors 26-28 are never rendered conductive at times that would
produce wrong-direction torque. As can be seen, if one considers
only the positive half-cycles of torque (each having a duration of
180.degree.-el.), the torque has a relatively uniform level only
during about 120.degree.-el. of the 180.degree.-el. half-cycle; for
the approximately 30.degree.-el. at the start and end of each
half-cycle, the potential torque contribution is far from being of
a steady value. Thus, as shown by the shaded areas, only the
120.degree.-el. intervals are actually employed; i.e., as shown by
the transistor conduction times in FIG. 4D, the respective ones of
the three phases are energized by current only at the times when
their torque contributions will be of a steady value.
It is emphasized that the manner of operation show in FIG. 4 is but
exemplary, it being the case that the motor produces only three
constituent torque pulses per 360.degree.-el. of rotor rotation,
with each torque pulse lasting only 120.degree.-el., not a full
180.degree.-el. Persons skilled in the art will understand that the
motor could furnish six such pulses if, for each phase, during the
120.degree.-el. time interval which is shifted by 180.degree.-el.
from the respective shaded area, the coil system were to be
energized by current of reversed direction, e.g. supplied to the
three phases by three further transistors or by other such
means.
The substantial closing up of the stator's surface facing the air
gap 16 by means of the auxiliary poles 19 is highly desirable,
because a large part of the rotor magnetic field crossing over in
the illustrated construction to the auxiliary poles would, upon
omission of the auxiliary poles, be pulled to the main poles 17 and
be added thereto. Functionally this would have the same effect as
if the pole faces 18 of the main poles 17 were substantially wider
than 180.degree.-el., which would be equivalent to chording.
Furthermore, strong jolting would occur. Both these effects are
avoided by means of the auxiliary poles 19. On the other hand,
however, the auxiliary poles 19 hinder the installation of the
non-overlapping coils 22, 23, 24 into the respective stator slots
34.
In order on the one hand to keep small the slot openings between
the main pole faces 28, but on the other hand to provide for
windability in a manner suited to fabrication needs, the auxiliary
poles in the three-phase brushless dc motor of FIG. 2 (where for
simplicity the rotor is not shown) are not stamped out together
with the main poles from the sheet metal of the stator's sheet
metal stack but instead are designed as separate pole bodies 36
which can be afterwards inserted into corresponding recesses 37 in
the stator's sheet metal stack. In this embodiment the main poles
17 are wound with the stator coils 22, 22', 23, 23' and 24, 24',
during which the pole bodies 36 forming the auxiliary poles 19 are
not yet inserted. Only after the winding of the main poles are the
pole bodies 36 pushed into the recesses 37 in order to
substantially close up the slot openings 39. The pole bodies 36
preferably consist of non-laminated, solid material. The pole
bodies 36 preferably consist of non-laminated, solid material. The
circumferential extent of 60.degree.-el. of the auxiliary poles is
relatively small compared to the circumferential extent of
180.degree.-el. of the main pole faces 18 and, in correspondence
thereto, they accept only a relatively small magnitude flux; as a
result, pole bodies 36 made from solid material do not lead to
substantial eddy-current losses. The pole bodies 36 can
advantageously be fabricated from sintered material, especially
sintered iron. The sintering process permits the manufacture of
dimensionally accurate shapes without subsequent machining.
Furthermore suitable for the pole bodies 36 are siliconized iron
types, such as for example commercially available from the
Vakuumschmelze Company under the trade name "Trafoperm".
The pole bodies 36 provided to form the unwound auxiliary poles 19
can advantageously be provided with recesses 40 (FIG. 3) to
accommodate the position sensors 30, 31, 32. Especially when the
pole bodies 36 are fabricated using a sintering technique, this
necessitates practically no further fabrication cost.
It is to be understood that, with the arrangement of FIG. 2, the
rotor can be designed in the same way as in the case of FIG. 1.
Whereas FIGS. 1 and 2 depict internal-rotor motors, it is
furthermore to be understood that the expedients described above
can with advantage be applied in the same way in the case of
external-rotor motors.
Concrete embodiments having been described above, the invention
itself is defined in the following claims.
* * * * *